The invention relates to a constant velocity universal joint designed as a fixed joint having an outer joint part provided with first meridional ball tracks, a ball hub provided with second meridional ball tracks, the center lines of the ball tracks each being undercut-free in the same axial projection. Balls are received in the associated first ball tracks and second ball tracks, a ball cage holding the balls in a common plane. A joint base is connected to the outer joint part and is positioned at the open end of the undercut-free ball tracks.
DE 31 32 364 Cl is an example of a constant velocity universal joint. In one axial direction, it comprises undercut-free ball tracks. The outer joint part is integrally connected to a wheel hub and has axially undercut calotte-shaped guiding faces for the cage. Such guiding faces require chip-forming machining or very complicated forming tools to permit non-chip-forming production. The joint base, in a broader sense, forms part of the wheel hub into which a plate metal cover is inserted.
Another constant velocity universal joint is known from DE 32 09 596 C2. It is provided with axially undercut-free ball tracks which open towards the joint base. The outer joint part has a supporting disc with an annular guiding face for a supporting element which fulfills the cage function only in one direction via pressure forces. To prevent the joint from being pulled apart there is provided a calotte-shaped guiding face directly between the cage and the outer joint part. In order to achieve a satisfactory articulation angle, the centers of curvature of the ball tracks have to be offset relative to each other by a relatively large amount. This results in the need for a thick supporting disc, which is disadvantageous. The tracks are subject to high forces, which results in a great deal of wear in the tracks and at the guiding faces of the supporting disc.
It is an object of the present invention to provide a constant velocity universal joint as initially mentioned in which the faces to be machined are reduced to a minimum. It is a further object of the invention to provide a constant velocity universal joint which can be machined very easily because of its shape, as a result of which production expenditure is reduced.
The present invention achieves these objectives in that the joint base is provided with internally positioned undercut-free guiding faces forming a contact region relative to a partial region of the outer face of the cage extending towards the joint base. The remaining partial regions of the inner face of the outer joint part positioned beyond or outside the contact regions are not in contact due to free space recesses set back relative to the outer face of the cage.
In a further embodiment, the ball hub is provided with externally positioned undercut-free guiding faces which form a contact region relative to a partial region of the inner face of the cage extending towards the joint aperture, the remaining partial regions of the outer face of the ball hub positioned outside the contact regions are provided with free space recesses set back relative to the inner face of the cage. The surface of the ball hub which forms these free space recesses, follows the root of the ball track and is dimensioned in such a way that the depths of the ball tracks in the ball hub are substantially constant.
By introducing these measures it is possible to provide a constant velocity universal joint in which only substantially reduced guiding faces at the outer joint part and, in some embodiments, equally reduced guiding faces at the ball hub need to be machined. Non-contacting partial regions of the ball hub do not require precision machining. The undercut-free guiding faces may be produced by simple processes in lieu of chip-forming processes. In one embodiment, the outer joint part and the joint base may be produced by simple tools by cold extrusion or similar non-chip-forming production methods.
In the region adjoining the guiding faces, a circumferential recess is provided at the outer joint part and at the ball hub relative to the cage, as a result of which the lubrication conditions at the cage may be improved. In consequence, the requirements for production accuracy may be less stringent.
With usual designs, the preferred assembly method consists of the inner joint part, with the axes extending perpendicularly relative to each other and making use of the ball tracks, being inserted into the ball cage and then turned into a coaxial position. This step is followed by the balls being inserted radially. The outer joint part is then slid on in a purely coaxial movement, with the joint base being positioned thereagainst also in a purely coaxial movement. The joint base and outer joint part may then be welded together for example or they may be connected to each other by a securing ring. Alternatively, they may be secured to each other by a rolled-on plate metal cap or the like. Because of the predominantly linear movements, the assembly process is suitable for being automated by using tools which are easily controlled.
Any tensile loads on the ball hub and outer joint part are accommodated through contact between the ball hub and the cage on the one hand, pressure applied by the cage window to the balls and contact between the balls and the tracks and thus pressure on the outer joint part on the other hand. In the case of a shear load between the ball hub and joint base, the balls are in contact with the tracks and are supported on the cage windows, the cage resting against the inner guiding faces of the joint base. In this case, too, the non-contacting partial regions of the outer joint part do not have to be machined.
According to a further embodiment, the outer joint part is internally expanded to form a cone in the direction of the joint base which is provided with an externally conical projection containing the undercut-free guiding faces formed therein. Radially outside the conical faces there are provided radial faces at the outer joint part and joint base.
At the joint base and outer joint part there may be provided complementary cylindrical centering faces radially outside the conical and radial faces on which the parts mutually center one another.
In one embodiment, upon contact between the balls and the ball tracks of the outer joint part and ball hub, the ball cage is axially inserted into the outer joint part and when the joint base is axially inserted until it contacts the ball cage, there should be an axial clearance between the outer joint part and the joint base. In this way, by taking into account any play in the cage windows, it is possible to set the smallest possible play between the cage and the guiding faces.
In a related embodiment, both the guiding face in the outer joint part, i.e. especially in the joint base, and the guiding face at the ball hub may be designed to be internally and, respectively, externally spherical while comprising the same radius of curvature as the corresponding contact face of the cage. However, this would be disadvantageous from the point of view of frictional forces. Therefore, in a more advantageous embodiment, the guiding faces in the outer joint part, i.e. in the joint base and at the ball hub, are rotational faces whose radius of curvature is greater than that of the contact face of the outer surface of the cage and smaller than that of the contact face of the inner face of tee cage. The inner guiding face in the joint base, especially towards the inner cone, may be designed with a radius of curvature that is infinite. With this further design it is possible to prevent the cage edges from being subjected to impermissible loads.
A particularly advantageous track shape is achieved if the center lines consist of circular sections an tangentially adjoining straight lines.
The radii of curvature of the spherical guiding faces may be slightly offset on the outside and inside of the cage, although this is not essential for the ball control effected by the tracks. As a result, there are obtained radially longer guiding faces for the balls within the cage window in order to ensure improved guiding conditions at large joint articulation angles.
With a decreasing control angle caused by an increasing articulation angle, there could be a loss of contact between the balls and the tracks. In order to prevent that the track cross sections in one embodiment are such that they ensure a so-called three-point contact, i.e. contact in the base region on the one hand and, depending on the direction of rotation, contact with one of the flanks on the other hand. An embodiment has a planar base for the cross section and two curved flanks, the radius of curvature being greater than that of the balls. The cross section of the tracks in the outer joint part always has to be the same as that of the tracks in the ball hub. A high degree of production accuracy is essential only in respect of the track base. Tolerances in the track flanks do not have a disadvantageous effect.
To ensure a lubricating effect during a relative movement between the cage and the outer joint part and ball hub respectively, the ball hub should be provided with inner free space recesses which increase axially inwardly in the direction of the joint base and which adjoin the inner guiding faces of the cage. The outer joint part, with gaps which adjoin the outer guiding faces of the cage and which are axially open towards the joint aperture, should be exposed relative to the radially inner cage.
From the following detailed description taken in conjunction with the accompanying drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.